// Physical memory allocator, for user processes,
// kernel stacks, page-table pages,
// and pipe buffers. Allocates whole 4096-byte pages.

#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "spinlock.h"
#include "riscv.h"
#include "defs.h"

void freerange(void *pa_start, void *pa_end);

extern char end[]; // first address after kernel.
                   // defined by kernel.ld.

struct run {
  struct run *next;
};

#define MAXPAGES ((PHYSTOP - KERNBASE)/PGSIZE)

struct {
  struct spinlock lock;
  struct run *freelist;
  char refcount[MAXPAGES];
} kmem;


char read_ref(uint64 pa) {
    return kmem.refcount[pa];
}
void acquire_reflock(void) {
    acquire(&kmem.lock);
}
void release_reflock(void) {
    release(&kmem.lock);
}
char modify_ref(uint64 pa, int cnt) {
    return kmem.refcount[pa] += cnt;
}

void
kinit()
{
  initlock(&kmem.lock, "kmem");
  memset(kmem.refcount, 1, sizeof kmem.refcount);
  freerange(end, (void*)PHYSTOP);
}

void
freerange(void *pa_start, void *pa_end)
{
  char *p;
  p = (char*)PGROUNDUP((uint64)pa_start);
  for(; p + PGSIZE <= (char*)pa_end; p += PGSIZE)
    kfree(p);
}

// Free the page of physical memory pointed at by v,
// which normally should have been returned by a
// call to kalloc().  (The exception is when
// initializing the allocator; see kinit above.)
void
kfree(void *pa)
{
  struct run *r;

    acquire(&kmem.lock);
  if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP || kmem.refcount[REFIDX(pa)] <= 0)
    panic("kfree");

  if(--kmem.refcount[REFIDX(pa)]) {
      release(&kmem.lock);
      return;
  }

  // Fill with junk to catch dangling refs.
  memset(pa, 1, PGSIZE);

  r = (struct run*)pa;

//  acquire(&kmem.lock);
  r->next = kmem.freelist;
  kmem.freelist = r;
  release(&kmem.lock);
}

// Allocate one 4096-byte page of physical memory.
// Returns a pointer that the kernel can use.
// Returns 0 if the memory cannot be allocated.
void *
kalloc(void)
{
  struct run *r;

  acquire(&kmem.lock);
  r = kmem.freelist;
  if(r)
    kmem.freelist = r->next;

  if(r) {
      memset((char *) r, 5, PGSIZE); // fill with junk
      if(kmem.refcount[REFIDX(r)])
          panic("kalloc: new page already has refcount!");
      kmem.refcount[REFIDX(r)] = 1;
  }
    release(&kmem.lock);
  return (void*)r;
}

void *kalloc_nolock(void) {
    struct run *r;

    r = kmem.freelist;
    if (r)
        kmem.freelist = r->next;
    if (r) {
        memset((char *) r, 2, PGSIZE);
        if (kmem.refcount[REFIDX(r)])
            panic("kalloc: new page already has reference count.");
        kmem.refcount[REFIDX(r)] = 1;
    }

    return (void *)r;
}